Known LED chips generate visible or non-visible light in a specific region of the light spectrum. The light output from the LED may be, for example, blue, red, green or non-visible ultra-violet (UV) or near-UV, depending on the material composition of the LED. When it is desired to construct an LED light source that produces a color different from the output color of the LED, it is known to convert the LED light output having a peak wavelength (the “primary light”) to light having a different peak wavelength (the “secondary light”) using photoluminescence.
The photoluminescence process involves absorbing the higher energy primary light by a wavelength-converting material such as a phosphor or mixture of phosphors thereby exciting the phosphor material, which emits the secondary light. The peak wavelength of the secondary light depends on the type of phosphor material, which can be chosen to provide secondary light having a particular peak wavelength. This process may be generally referred to as “wavelength conversion” and an LED combined with a wavelength-converting structure that includes wavelength-converting material, such as phosphor, to produce secondary light, may be described as a “phosphor-converted LED” or “wavelength-converted LED.”
Depending on the processing method and/or properties of the wavelength-converting material, at least a portion of the primary light and/or secondary light may be lost due to internal reflection, scattering, and/or absorption in the wavelength-converting structure. Further, for some wavelength-converting structures, e.g., powder phosphor or ceramic layer(s), multiple internal interfaces may impede heat transfer and therefore dissipation of heat produced by the LED and phosphor materials.